The present invention relates to a protection circuit for power management semiconductor devices for use in a semiconductor integrated circuit and a power converter having the protection circuit.
As a power management semiconductor device for use in a power converter, a bipolar/MOS composite type semiconductor device (IGBT (Insulated Gate Bipolar Transistor)) has been widely used in recent years. The IGBT has a characteristic that while the amount of collector current to flow is determined by a gate voltage and a collector voltage, an increasing rate in the collector current associated with an increase in the collector voltage suddenly becomes larger as the gate voltage increases.
When there occurs an arm short circuit or a load short circuit in the power converter, a line power voltage of the power converter is applied to the IGBT which is in ON operation and an excessive short circuit current flows due to above mentioned IGBT characteristic.
As a result, if a thermal break occurs due to the overcurrent, or even if the overcurrent is cut off in high-speed, a peak voltage caused by a circuit inductance during the cutting off is so big that the peak voltage may exceed the collector emitter voltage limit of the IGBT.
Therefore, a method for detecting a short circuit of the IGBT and protecting the IGBT is described in a patent JP-A-2-262826 corresponding to U.S. Pat. No. 5,210,479. The technology described in the patent determines that an IGBT is short-circuited when a gate voltage and a collector voltage of the IGBT are their respective reference values or over.
Furthermore, in a patent JP-A-2000-295838, a softly cutoff means for suppressing the generation of a peak voltage caused by a circuit inductance during cutting off is described.